This invention relates generally to internal combustion engines having electric-actuated fuel injectors that inject fuel into combustion chambers of the engine. More particularly it relates to a system and method that uses several variables, including injector control pressure and the duration of an injector-actuation signal applied to the fuel injectors, in a process that calculates the quantity of fuel injected by a fuel injector during an injection.
A known electronic engine control system comprises a processor-based engine controller that processes various data to develop fueling data for the engine. The fueling data represents a quantity of fuel that is to be introduced into the engine for combustion. That control system also includes an injector control module, or injector driver module, for operating fuel injectors that inject fuel into the engine in quantities corresponding to the fueling data. The fueling data is supplied to the injector control module from the engine controller, and the injector control module has its own processor for processing the supplied data to develop proper data for causing the fuel injectors to inject fuel in quantities corresponding to the fueling data calculated by the engine controller. For any one or more of various reasons that need not be discussed here, the injector control module may also make certain adjustments to the supplied data when the engine control strategy and/or injector calibration make it appropriate to do so.
The injector control module also comprises injector drivers each of which delivers an electric current signal to an electric actuator of the respective fuel injector. A fuel injector may have one or more electric actuators depending on its particular construction. The signal that is applied to a fuel injector to cause an injection of fuel is commonly referred to generically as a pulse width modulated signal. In the case of a fuel injector that has a single actuator, the actuating signal is a true pulse whose width sets the amount of time of an injection, and hence essentially determines the quantity of fuel that the fuel injector injects into the corresponding engine cylinder in consequence of that applied pulse. In the known engine controller that is being referred to, it is the injector control module that calculates the pulse width by processing the fueling data supplied to it by the engine controller.
The particular nature of the electric actuation of any particular fuel injector depends on the particular construction of the fuel injector. There is the single actuator type mentioned above. Another type of fuel injector, one for a compression-ignition internal combustion engine, comprises an intensifier piston for creating a high-pressure injection of fuel directly into an associated engine cylinder. The intensifier piston comprises a head of given end area exposed to a control fluid, oil for example, in a control chamber, and a plunger, or rod, of smaller end area exposed to liquid fuel in an injection chamber. The electric actuator comprises a spool valve that uses two electric actuators, i.e. solenoid coils, to control the introduction of pressurized control fluid into the control chamber and the draining of control fluid from the control chamber.
When an electric signal for initiating a fuel injection is applied to one of the two electric actuators for the spool valve, control fluid is introduced under pressure through one portion of the spool valve into the control chamber to downstroke the intensifier piston and cause fuel in the injection chamber to be injected under pressure from a nozzle of the fuel injector into an associated engine cylinder. The intensifier piston amplifies the pressure of the control fluid by a factor equal to the ratio of the head end area to the plunger end area to cause the amplified pressure to be applied to liquid fuel in the injection chamber. As a result, fuel is injected into a combustion chamber at a pressure substantially greater than the pressure of the control fluid.
When an electric signal for terminating the fuel injection is applied to the other electric actuator, the spool valve operates to terminate the downstroke of the intensifier piston and instead allow control fluid to drain from the control chamber through another portion of the spool valve so that the intensifier piston can then upstroke to re-charge the injection chamber with liquid fuel in preparation for the next injection.
Examples of fuel injectors having valves like those just described appear in U.S. Pat. Nos. 3,837,324; 5,460,329; 5,479,901; and 5,597,118.
Where a single electric actuator controls a fuel injector valve, the beginning of an electric pulse applied to the actuator initiates an injection, and the injection terminates when the pulse ends. The injection time is therefore set by the width, i.e. time duration, of the actual electric pulse applied to the injector actuator.
Commonly assigned U.S. Pat. No. 6,029,628 is an example of a fuel injector comprising two electric actuators that operate respective valve mechanisms. A supply valve mechanism is controlled by an electric supply valve actuator for selectively controlling flow of control fluid through a supply passage for downstroking an intensifier piston. A drain valve mechanism is controlled by an electric drain valve actuator for selectively controlling flow of control fluid through a drain passage. Each valve actuator is selectively operable independent of the other to selectively operate the respective valve mechanism independent of the other. Actuation of the supply valve mechanism while the drain valve mechanism is not being actuated initiates an injection, and the injection terminates when the drain valve mechanism is actuated.
The use of two electric signals, each applied to a respective one of the two actuators, to set the duration of a fuel injection is like that described previously for the fuel injector that has two actuators for operating a spool valve because the difference between the times at which the two actuators are actuated, rather than the time duration of an actual electric pulse, controls the duration of an injection. But the two signals in effect define a pulse width for operating the fuel injector that is equivalent to the pulse width of a single pulse signal that determines the injection time of a fuel injector that has only a single electric actuator. Hence, reference to pulse width in a generic context should be understood to include an actual pulse width of a single signal or an equivalent pulse width resulting from the use of one signal to initiate an injection and another signal to terminate the injection.
The known engine controller also contains one or more look-up tables that its processor uses to calculate the desired fueling data, which is then processed to calculate the widths of electric pulses that operate the fuel injectors. The look-up tables are derived from actual testing of fuel injectors. Fuel injectors are mapped for various combinations of values for injector control pressure and actuating signal pulse width. Each combination of values defines a corresponding value for desired fueling data. A sufficient number of combinations are needed to cover the relevant ranges of the variables, but the available size of the look-up tables ultimately determines how many combinations can actually be stored in memory of the controller.
While increasing look-up table size, and hence the number of combinations that can be stored, will endow the tables with a higher degree of resolution that may be desirable for increased fueling accuracy, the increased size of the electronic storage medium that is required to contain the stored data increases the cost of the controller. A greater amount of mapping is also required in order to obtain the greater amount of data.
A lesser number of stored combinations may decrease the resolution, and hence decrease fueling accuracy. The processor may then on occasion have to interpolate the mapped data in order to yield desired fueling data, and where non-linearity is present in the fuel injector, linear interpolation may not yield the accuracy that would be obtained from a larger table of greater resolution.
Regardless of fuel injector type or of how fuel injector data is mapped into a controller, fuel injector calibration is also important for securing desired fueling. Mass production methods inherently result in some variation in calibration from fuel injector to fuel injector, and while such methods may strive to minimize the range of these variations, the ranges remain significant enough that some classification of fuel injectors according to a number of different calibration categories, or groups, is appropriate in a mass production environment. The mapping of fuel injector data that has been described above may therefore represent mean data obtained from mapping a number of individual fuel injectors statistically representative of a universe of fuel injectors, in which case the calculated fueling data may be further processed to account for individual fuel injector calibration.
Hence, before it is assembled to an engine, a mass-produced fuel injector is operated to ascertain its actual calibration. The actual calibration determines into which particular one of a number of different calibration categories the fuel injector falls. The fuel injector is then identified by that particular category. When an engine is being manufactured, the associated engine controller is programmed in such a way that the particular calibration category of the fuel injector for each particular engine cylinder is made available to the controller. The controller uses that data to calibrate electric control signals to the fuel injectors, typically to secure injection of fuel in substantially equal quantities to each combustion chamber for a given value of fueling data calculated by the engine controller.
U.S. Pat. No. 5,575,264 discloses a method for associating actual performance data with a fuel injector. The data is contained in a medium, such as an EEPROM, that is mounted on the fuel injector body and that is suitable for reading by an associated engine controller.
U.S. Pat. No. 5,839,420 relates to a method for compensating a fuel injection system for fuel injector variability. Each fuel injector includes a storage medium that contains a calibration code identifying the actual calibration of the fuel injector. An associated engine controller converts a raw energizing time to a calibrated energizing time for each fuel injector based the calibration code for the fuel injector.
U.S. Pat. No. 5,634,448 relates to another method for trimming fuel injectors to compensate for fuel injector variability.
U.S. Pat. No. 4,402,294 relates to a system for calibrating fuel injectors.
Other patents that relate to systems and methods for calculating engine fueling and/or correcting the calculation for factors such as individual fuel injector calibration are U.S. Pat. No. 4,379,332; U.S. Pat. No. 4,619,234; and U.S. Pat. No. 5,806,497.
Given the significant effort that is needed to map and calibrate fuel injectors, and the amount of media needed to store a sufficient amount of mapped data to cover relevant ranges of variable parameters affecting engine fueling, as discussed above, it would be desirable to provide a system and a method that reduce the extent of the mapping effort and of the amount of data storage that is needed. It is toward these objectives that the present invention is directed.
The present invention relates to a system and method for calculating the quantity of fuel injected during an injection without using a look-up table, or tables, containing values of desired engine fueling correlated with various combinations of variable parameters, such as injector control pressure and actuating signal pulse width. Rather, the inventive system and method comprise processing variable parameters according to a formula that yields a resultant value of desired engine fueling. The processing is performed with sufficient speed by a processor to continually update the desired engine fueling in real time.
A related aspect concerns a system and method for deriving the formula, including the derivation of certain coefficients that are used in the formula.
Accordingly, a generic aspect of the present invention relates to a method of deriving a formula for calculating a quantity of fuel injected by an electric-actuated fuel injector during an injection wherein duration of the injection is set by duration of an electric signal applied to the fuel injector and pressure at which the fuel is injected is set by pressure of hydraulic fluid applied to the fuel injector. The method comprises mapping the fuel injector by applying, to the fuel injector, various combinations of different selected hydraulic fluid pressures and different selected durations of the electric signal. For each combination, the quantity of fuel injected is measured to create a corresponding data set for the combination that comprises the corresponding selected hydraulic fluid pressure, the corresponding selected electric signal duration, and the quantity of fuel injected in consequence of the application of the corresponding selected hydraulic fluid pressure and the corresponding selected electric signal duration to the fuel injector. Data from the data sets is processed to create terms of a multiple term mathematical formula that is used to calculate the quantity of fuel injected, wherein the terms of the formula include as variables, the electric signal duration and the hydraulic fluid pressure.
Another generic aspect of the present invention relates to a system for deriving a formula for calculating a quantity of fuel injected by an electric-actuated fuel injector during an injection wherein duration of the injection is set by duration of an electric signal applied to the fuel injector and pressure at which the fuel is injected is set by pressure of hydraulic fluid applied to the fuel injector. The system comprises apparatus for mapping the fuel injector by applying various combinations of different selected hydraulic fluid pressures and different selected durations of the electric signal to the fuel injector. For each combination, the quantity of fuel injected is measured to create a corresponding data set for the combination that comprises the corresponding selected hydraulic fluid pressure, the corresponding selected electric signal duration, and the quantity of fuel injected in consequence of the application, to the fuel injector, of the corresponding selected hydraulic fluid pressure and the corresponding selected electric signal duration. A processor processes data from the data sets to create terms of a multiple term mathematical formula for calculating the quantity of fuel injected, wherein the terms of the formula include as variables, the electric signal duration and the hydraulic fluid pressure.
Still another generic aspect of the present invention relates to an internal combustion engine comprising one or more electric-actuated fuel injectors each of which injects fuel into a respective combustion chamber of the engine as a function of injector control pressure and the duration of an electric actuating signal that sets the duration of a fuel injection to achieve an injection quantity determined at least in part by a desired fueling data representing desired fueling of the engine. An engine control system comprises one or more processors that calculate the desired fueling data, and from the desired fueling data, the duration of the electric actuating signal for each fuel injector. The calculation is performed by processing the desired fueling data and data representing injector control pressure, including processing, according to a mathematical formula, data correlated with the desired fueling data and data representing injector control pressure, to develop data that the control system further processes to calculate the duration of the electric actuating signal.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.